Hydrolysed proteins have been known for use as seasonings in food systems for centuries in the Far East in the form of soya sauce which traditionally has been prepared by enzymatic hydrolysis requiring a long period of time, usually several months, for preparation. In producing soya sauce, plant protein containing materials such as cooked soya beans or defatted soya flour together with carbohydrates are inoculated with Aspergilli and the solid culture is fermented for 2 days to make fermented koji during which time enzymes are produced which are able to hydrolyse protein and carbohydrates in the moromi stage. The fermented koji is mixed with a solution of common salt to give moromi which is fermented for 4 to 8 months by the activity of micro-organisms such as soya lactic acid bacteria and soya yeasts from which the soya sauce is obtained by removing the solids portion from the fermented moromi.
About 100 years ago, a more rapid method of hydrolysing proteins for producing seasonings was developed using hydrochloric acid in which the time required is only a few hours. However, in recent years, the use of acid hydrolysed plant protein (HPP) in culinary applications has been under criticism due to the presence of some chloro-compounds which arises from the acid process. Therefore, attempts have been made to develop HPP replacements which can be used as body-givers in culinary applications. Soya sauce is one such suitable replacement. However, owing to the differences in the raw materials and the processing methods involved, the two products, HPP and soya sauce, have some differences in terms of chemical composition and flavor profile. Dosage of soya sauce which can be used as an HPP replacement is limited due to its "fermented" note. The different processing procedures also result in a significant variation in the degree of hydrolysis of the protein containing material to the amino acids. Soya sauce has a lower amino acid content than HPP and this leads to a significantly weaker body in soya sauce than in HPP.
In European patent application EP-640,291-A1, a process is disclosed for the production of a seasoning based on modified standard soya sauce technology in which the fermented koji is treated, before forming the moromi, by a low temperature hydrolysis whereby the resultant seasoning has a stronger body than a standard soya sauce. In this process, a fermented protein koji, prepared from a protein containing material and a carbohydrate, is treated by hydrolyzing the fermented protein koji at a temperature of from 2.degree. to 25.degree. C. and a pH of from 4.5 to 10 for a period of from 6 hours to 28 days. In order to improve the organoleptic and color stability of the seasoning product, salt and yeast are conveniently added to the hydrolyzed fermented koji to form a moromi and the moromi is preferably fermented under aerobic or anaerobic conditions for a period of from 1 to 6 weeks, more preferably from 2 to 4 weeks.
We have now found, surprisingly, that if yeast is incorporated during the hydrolysis of the fermented protein koji, cohydrolysis occurs causing a decrease in the reducing sugar level so that the subsequent moromi stage is unnecessary. This has the advantage of shortening the whole production time by at least one week. In addition, the amount of salt in the seasoning product may be varied as desired, e.g., from 0 to 100% by weight based on the weight of the fermented protein koji.